Method and Apparatus for Protecting External Call References

1. A method for protecting a software program having an external library reference whereby call convention can be used to ensure call to the external library resolves to a correct instance of a function and that the selected instance has not been modified, the method comprising: receiving a digitally signed software program having a call to an external library, the call comprising an invariant target descriptor and a digital signature, wherein the digital signature comprises a hash of the external library encrypted by a recognized source of the software program; extracting the digital signature from the call; extracting the hash from the digital signature; using the invariant target descriptor to identify a first external library candidate; computing a hash of the first external library candidate; and comparing the extracted hash to the computed hash of the first external library candidate.

2. The method of claim 1 , wherein invariant target descriptor comprises a path to the external library.

3. The method of claim 1 , wherein the method is performed at bind-time.

4. The method of claim 1 , wherein the method is performed at run-time.

5. The method of claim 1 , further comprising, in response to the comparison, linking the first external library candidate software program.

6. The method of claim 1 , further comprising, in response to the comparison, generating an alert that the first external library target has been altered.

7. The method of claim 1 , wherein using the invariant target descriptor to identify a first external library candidate comprises searching a list of eligible objects and their location.

8. The method of claim 1 , wherein using the invariant target descriptor to identify a first external library candidate comprises traversing a search path.

9. The method of claim 1 , further comprising: using the invariant target descriptor to identify a second external library candidate; computing a hash of the second external library candidate; and comparing the extracted hash to the computed hash of the second external library candidate.